Pneumatic tire

ABSTRACT

A pneumatic tire comprises a carcass ply extending between bead portions and turned up around a bead core in each bead portion to form two turnup portion and a main portion therebetween; each of the turnup portion extends radially outwardly and adjoins the main portion from a certain height above the bead core; a space surrounded by the carcass ply main portion, each turnup portion and the bead core is filled with a small size bead apex rubber or a gus; and the bead portion is provided between the carcass ply and the bead core with a bead core cover for preventing the carcass cords from direct contacting with the bead core.

[0001] The present invention relates to a pneumatic tire, moreparticularly to a bead structure being capable of reducing the weight ofthe bead portions without deteriorating the bead durability.

[0002] In pneumatic tires used under relatively heavy loads such asheavy duty tires for trucks and buses, light truck tires and the like, alarge volume of bead apex rubber is disposed between a carcass plyturnup portion and main portion to increase the bead rigidity andthereby to decrease deformation of the tire under heavy loads.

[0003] Recently, in order to decrease tire weight, the bead structuresare reexamined, and many efforts have been made to decrease the weightof the bead portions by decreasing the volume of bead apex rubber.

[0004] In such tires of which bead apex rubber is very small, movementsand bending deformation of the carcass plies under loads are relativelylarge. Therefore, as the tension of the carcass cords is large and alarge stress concentrates on contacting points with the bead core, thecarcass cords are liable to be cut.

[0005] It is therefore, an object of the present invention to provide apneumatic tire, in which the carcass cords are prevented from being cutand the durability of the bead portions are improved.

[0006] According to one aspect of the present invention, a pneumatictire comprises

[0007] a tread portion,

[0008] a pair of sidewall portions,

[0009] a pair of bead portions with a bead core therein,

[0010] a carcass ply extending between the bead portions and turned uparound the bead core in each bead portion to form two turnup portion anda main portion therebetween,

[0011] each said turnup portion extending radially outwardly so as toadjoin the main portion from a certain height above the bead core,

[0012] a bead core cover disposed between the carcass ply and the beadcore for preventing cords of the carcass from direct contacting with thebead core, the bead core cover made of a textile fabric and/or a rubberlayer.

[0013] Preferably, the bead core cover is made of a textile fabric oforganic fiber yarn such as nylon, rayon, polyester and the like.

[0014] Embodiments of the present invention will now be described indetail in conjunction with the accompanying drawings.

[0015]FIG. 1 is a cross sectional view of a heavy duty tire according tothe present invention.

[0016]FIG. 2 is an enlarged cross sectional view of the bead portionthereof.

[0017]FIG. 3 is a cross sectional view showing the bead core and textilefabric.

[0018]FIG. 4 is a cross sectional view of a light truck tire accordingto the present invention.

[0019]FIG. 5 is an enlarged cross sectional view of the bead portionthereof.

[0020]FIG. 6 is a cross sectional view of a heavy duty tire according tothe present invention.

[0021]FIG. 7 is an enlarged cross sectional view of the bead portionthereof.

[0022]FIG. 8 is an enlarged cross sectional view showing a sealingstructure for a bead cavity.

[0023]FIG. 9 is an enlarged cross sectional view showing another exampleof sealing structure for the bead cavity.

[0024]FIG. 10 is a diagram for explaining the carcass cord distance inthe adjoining part.

[0025]FIG. 11 to FIG. 14 are diagrams for explaining a method ofmanufacturing a tire having the bead cavity.

DEFINITIONS

[0026] First, the terms used in this application “standard rim”,“standard pressure”, “standard load”, “bead base line” and “radialheight” are defined as follows:

[0027] Standard rim is the “standard rim” specified in JATMA, the“Measuring Rim” in ETRTO, the “Design Rim” in TRA or the like;

[0028] Standard pressure is the “maximum air pressure” in JATMA, the“Inflation Pressure” in ETRTO, the maximum pressure given in the “TireLoad Limits at Various Cold Inflation Pressures” table in TRA or thelike;

[0029] Standard load is the “maximum load capacity” in JATMA, the “LoadCapacity” in ETRTO, the maximum value given in the above-mentioned tablein TRA or the like;

[0030] Bead base line is an axial line passing the bead heel point atthe axially outer end of the bead bottom and corresponding to the rimdiameter; and

[0031] Radial height is a height measured radially from the bead baseline.

GENERIC DESCRIPTION

[0032] In the drawings, the tire 1 (1A, 1B, 1C) according to the presentinvention comprises a tread portion 2, a pair of sidewall portions 3, apair of axially spaced bead portions 4 with a bead core 5 therein, acarcass 6 extending between the bead portions 4, a belt 7 disposedradially outside the carcass 6 in the tread portion 2.

[0033] The belt 7 comprises at least one ply, preferably at least twocross plies of parallel cords.

[0034] For the belt cords, high-elastic-modulus cords such as steel cordare preferably used. But, organic fiber cords, e.g. nylon, aromaticpolyamide, rayon and the like can be used.

[0035] The bead core 5 is made of at least one inextensible material,for example, a coiled rubberized steel wire or wires, a coiledhigh-elastic-modulus organic cord or cords such as aromatic polyamidefiber cord, a wound tape-like material, and the like. As to thesectional shape of the bead core 5, a hexagonal shape is preferablyused. In case of heavy duty tires to be mounted on a 15-degrees taperrim, a hexagonal shape, of which aspect ratio is low and the major axisis inclined at the substantially same angle (10 to 17 degrees) as theinclination of the rim seat (15 degrees), is preferably used.

[0036] The bead core 5 is covered with a bead core cover made of atextile fabric 19 and/or a rubber layer 16 to prevent the carcass cords21 from direct contacting with the bead wire.

[0037] The carcass 6 comprises at least one ply 9 of cords 21 arrangedradially at an angle of 70 to 90 degrees with respect to the tireequator CO, and extending between the bead portions 4 through the treadportion 2 and sidewall portions 3, and turned up around the bead core 5in each bead portion 4 from the inside to outside of the tire to form apair of carcass ply turnup portions 9B and a main portion 9Atherebetween.

[0038] For the carcass cords 21, steel cords are preferably used in caseof heavy duty tires. However, organic fiber cords, e.g. nylon, rayon,polyester, aromatic polyamide and the like can be used.

[0039] As to the carcass ply turnup portions 9B, the distance from thecarcass ply main portion 9A gradually decreases towards the radiallyoutside from the bead core 5, and then, from a certain radial height(h), the distance becomes a substantially-constant minimum value. Thispart (hereinafter adjoining part 15) in which the distance between theturnup portion 9B and the main portion 9A is minimum and thus theseportions adjoin each other has a certain length L2.

[0040] Further, a part of the turnup portion 9B between a point at whichthe carcass ply turnup portion 9B comes into contact with the bead core5 and a point corresponding to the radially inner end of the adjoiningpart 15 is curved towards the axially inside. But, in the adjoining part15, it extends substantially straight along the carcass ply main portion9A. The carcass turnup portion 9B terminates at a position radiallyinside the maximum tire width point.

[0041] As to the carcass ply main portion 9A, a part which extendsradially outwardly from a point at which the carcass ply main portion 9Acomes into contact with the bead core 5, is formed substantiallystraight. This straight part Y extends to the radially inner end of theadjoining part 15 at least, usually to the radially outer end of theadjoining part 15, whereby the carcass cord path is minimized to controlthe axially outward movement or deformation of the carcass when the tireis loaded. Thus, the deformation of the bead portion can be reduced.

[0042] A space defined as surrounded by the carcass ply turnup portion9B and main portion 9A and the bead core 5 is filled with a small sizebead apex rubber 10 or a gas (usually air).

[0043] The bead portion 4 is provided along the bottom and axiallyoutside thereof with a chafer 11.

[0044] The chafer 11 is made of a relatively hard rubber having a 100%modulus of from 55 to 75 kgf/sq.cm, whereas the sidewall rubber 10 has a100% modulus of from 10 to 20 kgf/sq.cm. The chafer 11 extends radiallyoutwards from the underside of the bead core 5, with abutting on theaxially outside of the carcass 6. The chafer rubber 11 tapered-overlapsthe sidewall rubber 10 above the radially outer end of the rim flangeJf. In the overlapped portion, the chafer rubber 11 is positioned on theaxially inside of the sidewall rubber 10. On the outer surface of thetire, the radial height L4 of the radially outer edge of the chaferrubber 11 is preferably set in the range of from 1.2 to 2.5 times theflange height H.

[0045] If the height L4 is more than 2.5 times H, heat generationincreases and cracks are liable to occur on the surface chafer rubber11, and as a result, the bead durability decreases. If less than 1.2times H, the radially inner end portion of the sidewall rubber 10 isliable to wear.

[0046] If the 100% modulus of the chafer rubber 11 is less than 55kgf/sq.cm, the bead rigidity is insufficient. If more than 75 kgf/sq.cm,a heat generation increases and the bead durability decreases.

[0047] If the 100% modulus of the sidewall rubber 10 is less than 10kgf/sq.cm, it is difficult to protect the carcass 6 from externalinjuries. If more than 20 kgf/sq.cm, cracks are liable to occur on thesidewall surface.

First Embodiment

[0048]FIG. 1 and FIG. 2 show a heavy duty radial tire 1A according tothe present invention, wherein a state of the tire mounted on a standardrim J (a center drop 15-degree taper rim) and inflated to an internalpressure of 50 kpa is shown.

[0049] In this embodiment, the bead core 5 is made of a coiledrubberized wire, the sectional shape of which is a hexagon of a lowaspect ratio and the major axis thereof is inclined at the substantiallysame angle as the inclination of the rim seat (15 degrees).

[0050] The bead core 5 is covered with a bead core cover made of atextile fabric 19 so as to prevent the carcass cords 21 from directcontacting with the bead wire.

[0051] The textile fabric 19 is made of organic fiber yarn such asnylon, rayon, polyester and the like. Preferably, the yarn is relativelythin (for example, 940 dtex/2 to 1670 dtex/2) in comparison with theusual tire cords. It is possible to cover the bead core surfacepartially, but in this example, as shown in FIG. 3, the textile fabric19 is wound around the bead core 5 in a single layer at least,preferably a double layer, so as to cover all the surface of the beadcore 5.

[0052] The carcass 6 is composed of a single ply 9 of steel cordscomprising a pair of turnup portions 9B and a main portion 9A.

[0053] The distance of the carcass ply turnup portion 9B from the mainportion 9A becomes a minimum value from a radial height (h) and theadjoining part 15 extends a length H of from 35 to 70 mm. In theadjoining part 15, the rubber thickness measured from the cords of theturnup portion 9B to the cords of the main portion 9A, is set in therange of from 0.5 to 4.0 mm to effectively mitigate a sharing forcetherebetween.

[0054] The space surrounded by the carcass ply turnup portion 9B andmain portion 9A and the bead core 5 is filled with a bead apex 10.

[0055] The bead apex 10 is made of a relatively hard rubber having aJIS-A hardness of 70 to 100 degrees tapering towards the radiallyoutside from the bead core 5. The radial height (h) of the radiallyouter end 13 thereof is set in the range of 0.1 to 0.3 times, preferablynot more than 0.25 times, more preferably not more than 0.20 times theradial height Hk of the outer surface of the carcass 6 at the tireequator CO.

[0056] By the straight part Y of the carcass ply main portion 9A and thecurved part of the turnup portion 9B, the thickness of the bead apexrubber 10 is decreased. As a result, the turnup portion 9B comes near astress neutral line thereby greatly decreasing the compressive stress.

[0057] The belt 7 in this embodiment is compose of four plies 7A, 7B, 7Cand 7D of parallel steel cords disposed in this order from the inside tooutside. The cord angle of the first ply 7A is 50 to 70 degrees, and theangles of the second, third and fourth plies 7B to 7D are 10 to 30degrees with respect to the tire equator CO. The inclinations of thecords with respect to the tire equator CO are reversed between thesecond and third belt plies 7B and 7C.

Comparison Test 1

[0058] Heavy duty tires of size 11R22.5 14PR having the structure shownin FIG. 1 and FIG. 2 were prepared and tested for bead durability.

[0059] Bead durability test: Using a tire test drum, each test tire wassubjected to a 600 hour continuous running test under the followingconditions, and the running time to any bead damage was measured.

[0060] Running speed: 20 km/h

[0061] Tire load: 300% of standard load=9,000 kg

[0062] Tire pressure: standard pressure of 800 kpa,

[0063] Wheel rim: 22.5×8.25 standard rim

[0064] The specifications of the tires and test results are shown inTable 1. TABLE 1 Tire Ref.A1 Ex.A1 Ex.A2 Ex.A3 Ex.A4 Carcass Height Hk(mm) 211 211 211 211 211 Straight part of main portion exist exist existexist exist Adjoining part length L2 (mm)  40  40  40  40  40 Bead apexrubber JIS-A hardness (deg.)  90  90  90  90  90 Height h (mm)  40  40 40  40  40 Textile fabric — nylon nylon nylon nylon — 940dtex/2940dtex/2 1670dtex/2 1670dtex/2 Layer — single double single double Beaddurability (hrs.) 500 550 600 580 600

Second Embodiment

[0065]FIG. 4 and FIG. 5 show a light truck tire 1B according to thepresent invention, wherein a state of the tire mounted on a standard rimJ and inflated to an internal pressure of 50 kpa is shown.

[0066] The belt 7 is composed of at least two cross plies, in thisexample, two cross plies 7B and 7C of high-elastic-modulus cords such assteel cords and the like.

[0067] The bead core 5 is made of a rubberized steel wire coiled in ahexagonal sectional shape.

[0068] The carcass 6 comprises one to three plies, in this example twoplies 9 and 14 of organic fiber cords 21, e.g. polyester, rayon, nylon,aromatic polyamide and the like arranged at an angle of 75 to 90 degreeswith respect to the tire equator CO.

[0069] The inner carcass ply 9 consists of a pair of turnup portions 9Bturned up around the bead core 5 from the inside to outside of the tireand a main portion 9A therebetween. The outer carcass ply 14 hashowever, no turned up portion. The outer carcass ply 14 is disposed onthe inner carcass ply 9 so as to cover the outside of the main portion9A and the outside of the turnup portions 9B, and terminates axiallyoutside or beneath the bead core 5.

[0070] Similar to the former tire 1A, a substantially straight part Y ofthe carcass ply main portion 9A, a curved part of the carcass turnupportion 9B, and an adjoining part 15 of the carcass ply main portion andturnup portion are formed.

[0071] In this embodiment, the space surrounded by the carcass plyturnup portion 9B and main portion 9A and the bead core 5 is filled witha bead apex 10.

[0072] The bead apex 10 is made of a relatively hard rubber having aJIS-A hardness of 70 to 100 degrees tapering towards the radiallyoutside from the bead core 5. The radial height (h) of the radiallyouter end 13 thereof is set in the range of from H −15 mm to H +15 mm,wherein H is the rim flange height.

[0073] The height (h) in this tire 1B is lower than that of the formertire 1A. In such a tire, during building the tire, the carcass plyturnup portion is liable to come off the outer end of the bead apexrubber 10. In the finished tire, therefore, adhesive failure is liableto occur and air remains in this position which greatly decrease thebead durability.

[0074] In order to avoid this problem, as shown in FIG. 5, a firstrubber layer 16 is disposed between the carcass 6 and the axially innerand outer surfaces of the bead apex 10.

[0075] The first rubber layer 16 has a JIS-A hardness of 50 to 80degrees which is smaller than the JIS-A hardness of the bead apex rubberand a substantially constant thickness T1 of 1.0 to 3.0 mm.

[0076] In this example, the first rubber layer 16 extends continuouslyfrom the axially inside to outside of the bead apex 10 through theunderside of the bead core 5. Thus, the first rubber layer 16 is alsodisposed between the carcass and bead core, whereby the carcass cordscan be prevented from direct contacting with the bead core, and a sharpbend of the carcass cords at the corners of the bead core is prevented.Thus, carcass cord cuts can be effectively controlled.

[0077] Incidentally, it is possible to use such rubber layer and theabove-mentioned textile fabric 19 at the same time.

[0078] In this example, further, the first rubber layer 16 extendscontinuously from both the axially inside and outside of the bead apex10 to the adjoining part 15. In other words, a second rubber layer 17having a thickness T2 of 2.0 to 6.0 mm (two times T1) and a JIS-Ahardness of 50 to 80 degrees is disposed between the carcass ply mainportion 9A and turnup portion 9B in the adjoining part 15. The length L1of the second rubber layer 17 measured along the carcass 6 is preferablyset in the range of from 5 to 15 mm.

[0079] If the thickness T1 is less than 1.0 mm, it is difficult toprevent the carcass cords from being cut. If the thickness T1 is morethan 3.0 mm, the engaging force between the tire and rim becomesinsufficient.

[0080] If the thickness T2 is less than 2.0 mm, and/or the length L1 isless than 5 mm, it is difficult to eliminate the air and an adhesivefailure is liable to occur. If the thickness T2 and length L1 are morethan 6.0 mm and 15 mm, respectively, the weight increases against theprimary object.

[0081] In this embodiment, the chafer 11 extends radially outwards, withabutting the axially outside of the outer carcass ply 14.

Comparison Test 2

[0082] Light truck tires of size 7.00R16 having the structure shown inFIG. 4 and FIG. 5 were prepared and tested for the bead durability.

[0083] Bead durability test: Using a tire test drum, each test tire wassubjected to a 600 hour continuous running test under the followingconditions, and the running time to any bead damage was measured.

[0084] Running speed: 20 km/h

[0085] Tire load: 1100 kg

[0086] Tire pressure: 600 kpa

[0087] Wheel rim: 5.50F×16 standard rim

[0088] The specifications of the test tires and test results are shownin Table 2. TABLE 2 Tire Ref.B1 Ref.B2 Ex.B1 Carcass Straight part ofmain portion non exist exist Adjoining part length L2 (mm) — 40 40 Beadapex rubber JIS-A hardness (deg.) 90 90 90 Height h (mm) 85 28 28 Flangeheight H (mm) 12.7 12.7 12.7 Rubber layer 16 Thickness T1 (mm) — — 2JIS-A hardness (deg.) — — 70 Thickness T2 (mm) — — 4 Length L1 (mm) — —10 JIS-A hardness (deg.) — — 70 Bead durability (hrs) 400 500 600

Third Embodiment

[0089]FIG. 6 and FIG. 7 shows a heavy duty radial tire 1C according tothe present invention, wherein a state of the tire mounted of a standardrim J and inflated to a standard pressure but loaded with no tire loadis shown.

[0090] In this embodiment, the belt 7 is compose of four plies 7 a, 7 b,7 c and 7 d of parallel steel cords disposed in this order from theinside to outside. The cord angle of the first ply 7 a is 50 to 70degrees, and the angles of the second, third and fourth plies 7 b to 7 dare not more than 30 degrees with respect to the tire equator CO.

[0091] The bead core 5 is made of a coiled rubberized wire, thesectional shape of which is a low aspect ratio hexagon as explained inthe tire 1A. And the bead core 5 is covered with a bead core cover madeof a textile fabric 19.

[0092] The carcass 6 comprise a single ply 9 of steel cords arranged atsubstantially 90 degrees with respect to the tire equator C.

[0093] Similar to the former tires 1A and 1B, a substantially straightpart Y of the carcass ply main portion 9A, a curved part 12 of thecarcass turnup portion 9B, and an adjoining part 15 of the carcass plymain portion and turnup portion are formed. The curved part 12 extendsaxially inside or on a straight line X, the straight line X drawnbetween the axially outmost point BP of the bead core 5 and the outerend 8 e of the cavity 8.

[0094] In this embodiment, the space surrounded by the carcass plyturnup portion 6B and main portion 6A and the bead core 5 is not filledwith a bead apex rubber. The space is filled with a gas, usually air toform a cavity 8.

[0095] As shown in FIG. 7, the cavity 8 tapers towards the radiallyoutside from the bead core 5. The radial height (h) of the outer end 8 ethereof is 0.7 to 3.0 times the radial height H of the rim flange Jf. Ifthe height (h) is more than 3.0 times the height H, the bead durabilityand bead rigidity decrease.

[0096] The internal pressure of the cavity 8 is set to be more than anatmospheric pressure.

[0097] In order to maintain the internal pressure, the cavity 8 issurround by an airtight rubber layer 20 (20A, 20B).

[0098] In FIG. 6 and FIG. 7, along the inside of the cavity 8, a sealinglayer 20B is disposed.

[0099] The sealing layer 20B is preferably made of a butyl rubbercontaining not less than 30 phr of halogenated butyl rubber. Thethickness Ta of the sealing layer 20B is at least 0.2 mm. Especially,when the halogenated butyl rubber content is minimum, it is better touse a thicker layer. Preferably, the thickness Ta (mm) is determined asbeing not less than 20 times the halogenated butyl rubber content (phr).And, the thickness Ta is not more than 1.5 mm and not more than 50 timesthe halogenated butyl rubber content (phr).

[0100] As shown in FIG. 8, when the topping rubber layer 20A of thecarcass ply and bead core is very thin and/or the topping rubber is anon-butyl rubber whose principal component is diene rubber, the sealinglayer 20B is preferably disposed. However, when the topping rubber layer20A is thick enough to provide airtightness, the sealing layer 20B maybe omitted. Incidentally, the thickness of the topping rubber 20A is inthe range of 0.15 to 1.0 mm.

[0101]FIG. 9 shows another example of the sealing structure, wherein thesealing layer 20B extends beneath the bead core 5 so as to wrap the beadcore therein.

[0102] The adhesion of the butyl rubber layer 20B is not so good whencompared with the topping rubber. Therefore, to prevent separation,inserting length L5 of the sealing layer 20B between the carcass plymain portion 9A and turnup portion 9B is set to be not more than 5 mm.Further, the radial height L6 of the upper end of the sealing layer 20Bis preferably not more than 3.0 times the flange height H.

[0103] As shown in FIG. 10, in the adjoining part 15, the rubberthickness N between the carcass cords 21 of the main portion 9A and thecarcass cords 21 of the turnup portion 9B is set in the range of from0.15 to 4.5 times, preferably 1.3 to 3.5 times the diameter K of thecarcass cords 21. If the thickness N is less than 0.15 times K, it isdifficult to mitigate the sharing force, and there is the danger inwhich the carcass cords 21 directly contact with each other, and thus acarcass ply separation is caused. If the thickness N is more than 4.5times K, the turnup portion 9B is liable to be broken by a compressivestress and the heat generation is liable to increase.

[0104] In this example, to provide the thickness N, a cushion rubberlayer 22 having substantially same hardness as the topping rubber isdisposed between the carcass ply main portion 9A and turnup portion 9B.However, it is also possible to use the carcass ply topping rubberitself.

[0105] The length L2 of the adjoining part 15 is in the range of from0.5 to 5.0 times preferably 1.0 to 4.0 times the maximum section widthBW of the bead core 5. If the length L2 is less than 0.5 times BW, thebead durability decreases. If the length L2 is more than 5.0 times BW,it is difficult to improve the bead durability, and the tire surface isliable to undulate and a carcass ply edge separation is liable to occurbecause the outer end of the turnup portion 9B reaches to a positionwhere the sidewall rubber is relatively thin.

[0106] In this embodiment, the chafer 11 extends radially outwards, withabutting the axially outside of the turnup portion 9B, to a radialheight L3, wherein the height L3 is more than the radial height (h) ofthe cavity. As a result, the bead rigidity is increased, and therebyrunning performance such as steering stability and the like can beimproved.

Comparison test 3

[0107] Heavy duty radial tires of size 11R22.5 having the structureshown in FIG. 6 and FIG. 9 were prepared and tested for the beaddurability, steering stability and tire weight. The test tires had acarcass composed of a single ply of steel cords (3×0.17+7×0.20) arrangedat an angle of 90 degrees with respect to the tire equator at a cordcount of 21 (/5 cm) at the tread center, and a belt composes of fourplies of steel cords (3×0.20+6×0.35) laid parallel with each other at acord count of 26 (/5 cm). The cord angles of the four plies were+67/+18/−18/−18 degrees (from inside to outside).

[0108] Bead durability test: Using the tire test drum, each test tirewas subjected to a 10000-kilometer continuous running test under thefollowing conditions, and the running distance Li to any visible damagewas measured.

[0109] Running speed: 20 km/h

[0110] Tire load: 9000 kgf

[0111] Tire pressure: 1000 kPa

[0112] Wheel rim: 8.25×22.5 standard rim

[0113] In Table 3, the ratio of the distance Li to 10000 kilometers isindicated by an index based on Reference tire C being 100.

[0114] Steering stability test: Running a 10-ton truck provided on allthe wheels with test tires on an asphalt road, the test driver evaluatedthe steering response, rigidity, road grip and the like. The results areindicated by an index based on reference tire C being 100, wherein thelarger the index, the better the steering stability.

[0115] Tire pressure: 800 kPa

[0116] Wheel rim: 8.25×22.5 standard rim

[0117] Tire weight: In Table 3, the tire weight is indicated by an indexbased on Reference tire being 100.

[0118] The specifications of the test tires and test results are shownin Table 3. TABLE 3 Tire Ex. C1 Ex. C2 Ex. C3 Ex. C4 Ex. C5 Ex. C6 Ex.C7 Ex. C8 Ex. C9 Ex. C10 Ref. C Cavity height h (mm) 28 40 28 28 28 2828 28 28 28 — Ratio h/H 2.2 3.1 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 —Sealing rubber layer Thickness Ta (mm) 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.80.8 0.8 — Thickness T (mm) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 —Inserting Length L5 (mm) 3.0 3.0 6.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 —Carcass Adjoining part Length L2 55 55 55 7 55 55 55 55 55 55 55 (mm)Ratio L2/BW 3.7 3.7 3.7 0.4 5.2 3.7 3.7 3.7 3.7 3.7 3.7 Rubber thicknessN (mm) 1.3 1.3 1.3 1.3 1.3 0.1 3.6 1.3 1.3 1.3 1.3 Ratio N/K 1.7 1.7 1.71.7 1.7 0.13 4.7 1.7 1.7 1.7 1.7 Chafer Height L3 (mm) 65 65 65 65 65 6565 25 25 25 25 100% modulus (kgf/sq.cm) 60 60 60 60 60 60 60 60 54 76 60Test Results Bead durability 150 105 130 102 150 80 101 75 105 110 100Steering stability 105 103 105 100 105 103 100 90 95 100 100 Tire weight98 97 98 96 103 97 102 98 98 98 100

[0119] From the test results, it was confirmed that test tires accordingto the present invention can be improved in the bead durability andweight wile maintaining the steering stability.

Tire Manufacturing Method

[0120]FIG. 11 to FIG. 14 show a method of manufacturing the tire 1Chaving the cavity 8.

[0121] First, an inner liner rubber 30 is wound around a tire buildingdrum 40. On each side of the inner liner rubber 30, a strip of rubber 31made up of a chafer rubber 11 and a sidewall rubber 10 connected witheach other, is further wound. Further, a carcass ply 9 is wound thereonto form a cylindrical main body 32. A pair of annular bead cores 5 areput around the cylindrical main body 32, and a bead lock 43 is expandedto fix the bead core, wherein the bead core is covered with a textilefabric 19 in advance. Further, a butyl rubber seat for the sealing layer20B is wound over the bead core 5. Here, the tire building drum 40comprises a central former 42 and a pair of side formers 41. The centralformer 42 can be expanded, for example, by means of inflation of abladder, and also, the side former 41 can be expanded by means ofinflation of a bladder. Further, a tread ring 36 made up of a treadrubber 35 and a belt 7 which are assembled beforehand is put around thecarcass main portion. Next, as shown in FIG. 13, the central former 42and side formers 41 are expanded in order that the carcass main portionis shaped in a toroidal shape, and the carcass turnup portions 9B andthe rubber strip 31 is fold around the bead core 5 onto the carcass mainportion 9A. By the expansion of the carcass main portion 9A, the carcassmain portion 9A is pressed against the tread ring 36. The raw tire 1Cbuilt up as above is put in a mold and vulcanized by applying heat andpressure. During the vulcanizing process, the cavity 8 is provided withan internal pressure of over an atmospheric pressure.

[0122] As explained above, the present invention can be suitably appliedto heavy duty tires and light truck tires. However, it is also possibleto apply passenger car tires and the like.

1. (Amended) A pneumatic tire comprising a tread portion, a pair ofsidewall portions, a pair of bead portions with a bead core therein, acarcass comprising a carcass ply extending between the bead portions andturned up around the bead core in each bead portion to form two turnupportion and a main portion therebtween, each said turnup portionextending radially outwardly and adjoin the main portion from a certainheight (h) above the head core so as to form an adjoining part, a beadcore cover disposed between the carcass ply and the bead core forpreventing cords of the carcass from direct contacting with the beadcore, the bead core cover made of a textile fabric and/or a rubberlayer, a space in each bead portion surrounded by the carcass ply mainportion, the turnup portion and the bead core filled with a bead apexrubber, the bead apex rubber having a JIS-A hardness of 70 to 100degrees and tapering radially outwardly from the bead core, the radiallyouter end of the bead apex disposed at said height (h) being in a rangeof from H−15 mm to H+15 mm, wherein H is the height of a flange of awheel rim.
 2. The pneumatic tire according to claim 1 , wherein the beadcore cover is made of a textile fabric of organic fiber yarn.
 3. Thepneumatic tire according to claim 1 , wherein a space in each beadportion surrounded by the carcass ply main portion, the turnup portionand the beat core is filled with a bead apex rubber tapering radiallyoutwardly from the bead core.
 4. The pneumatic tire according to claim 3, wherein the bead apex rubber has a JIS-A hardness of 70 to 100degrees, and the height of the bead apex rubber is set in the range of0.1 to 0.3 times the height of the carcass.
 5. (Amended) The pneumatictire according to claim 3 , wherein the bead apex rubber has a JIS-A of70 to 100 degrees, the height of the bead apex rubber is in the range offrom H−15 mm to H+15 mm, wherein H is the height of a flange of a wheelrim for the tire, and between the bead apex rubber and the carcass, arubber layer having a JIS-A hardness being in the range of from 50 to 80degrees and being less than that of the bead apex rubber and having athickness of from 1.0 to 3.0 mm is disposed.
 6. The pneumatic tireaccording to claim 1 , wherein a space in each bead portion surroundedby the carcass ply main portion, the turnup portion and the bead core isfilled with a gas to form a cavity.
 7. The pneumatic tire according toclaim 6 , wherein said cavity is surrounded by a gas-tight rubber layer.8. The pneumatic tire according to claim 7 , wherein the gas-tightrubber layer is made of butyl rubber.
 9. The pneumatic tire according toclaim 6 , wherein the cavity tapers towards the radially outside fromthe bead core, and the height of the cavity is in the range of from 0.7to 3.0 times the height of a flange of a wheel rim for the tire.
 10. Thepneumatic tire according to claim 2 , wherein a space in each beadportion surrounded by the carcass ply main portion, the turnup portionand the bead core is filled with a bead apex rubber tapering radiallyoutwardly from the bead core.
 11. The pneumatic tire according to claim2 , wherein a space in each portion surrounded by the carcass ply mainportion, the turnup portion and the bead core is filled with a gas toform a cavity.
 12. The pneumatic tire according to claim 7 , wherein thecavity tapers towards the radially outside from the bead core, and theheight of the cavity is in the range of from 0.7 to 3.0 times the heightof a flange of a wheel rim for the tire.
 13. The pneumatic tireaccording to claim 8 , wherein the cavity tapers towards the radiallyoutside from the bead core, and the height of the cavity is in the rangeof from 0.7 to 3.0 times the height of a flange of a wheel rim for thetire.